The overall objective is to determine the acceptability, efficacy and safety of dietary intervention in 100 previously untreated healthy boys and girls, ages 8-10 years, with primary elevations in the plasma level of low density lipoprotein (LDL) cholesterol, for a long-term (four years) period as part of a national collaborative full scale clinical trial. Of 16,359 pupils in the 3rd, 4th, and 5th grades in the Baltimore County Public School System, cholesterol screening (Visit0) will be performed on about 2,400 children. Children with hypercholesterolemia will be asked to undergo a pre-randomization evaluation at three clinic visits (V-1, V-2, V-3) including detailed biochemical, psychological, physical, and anthropometric assessment. Fifty children will be randomized into the experimental group and 50 into the control group. Both groups will be instructed on a prudent diet reduced in total and saturated fat, cholesterol, and somewhat enriched in polyunsaturated fat. The control group will remain on this diet and be seen yearly. After six months, the experimental group will be reinstructed on a more restrictive diet and be seen every two months to facilitate compliance and education. The efficacy and safety of the diets will be assessed by determining the plasma levels of lipids, lipoproteins and apoproteins and the clinical nutritional status, including anthropometric measures, biochemical tests including minerals and vitamins, nutrient intake, bone age, physical examination and Tanner's score. Possible adverse consequences on cognitive, emotional and behavioral functioning will be studied. Intra-individual trends with time as well as inter-group comparisons will be performed. Our hypothesis is that such diets will be acceptable, safe and effective in long-term lowering of total and LDL cholesterol.